In the semiconductor processing system which manufactures a semiconductor device and the like, the target substrate such as a semiconductor wafer is transferred. For example, the wafer is transferred through a clean atmosphere under atmospheric pressure or vacuum pressure and loaded into a process chamber. Further, the wafer is inversely unloaded from the process chamber and transferred to a predetermined location. A transfer apparatus to transfer the semiconductor wafer is disclosed in, e.g., the following patent documents 1 to 4.
FIG. 33 is a perspective view showing an example of a conventional transfer apparatus of the same type as that of the apparatuses disclosed in patent documents 1 and 3. A transfer apparatus 2 has an arm 8 obtained by coupling a proximal end arm 4 and intermediate arm 6, so that it can bend and stretch. A pick arm 10 is pivotally attached to the distal end of the arm 8. Pick portions 10A and 10B are formed at the two ends of the pick arm 10. The entire arm 8 can rotate integrally. When the arm 8 is bent or stretched, the driving force is transmitted by a pulley incorporated in the arm 8 and a coupling belt to retreat or advance the pick arm 10 in a predetermined direction.
Two motors (not shown) are disposed in a motor source 12 which drives the transfer apparatus 2. The first motor rotates the entire arm 8 as described above to face it in a desired direction. The second motor bends or stretches the arm 8 as described above.
When the transfer apparatus 2 is used, semiconductor wafers W in the process chamber can be exchanged in the following manner. More specifically, first, one pick of the pick arm 10, e.g., the pick portion 10A, is emptied, and an unprocessed wafer W is held by the other pick portion 10B. Subsequently, the arm 8 is bent or stretched to unload a processed wafer W from the process chamber. Then, the empty pick portion 10A is advanced into the process chamber to receive the processed wafer W. The pick portion 10A is then retreated to unload the processed wafer W from the process chamber.
Subsequently, with the arm 8 being folded as shown in FIG. 33, the entire arm is rotated through 180° to direct the pick portion 10B which holds the unprocessed wafer W toward the process chamber. The arm 8 is then bent or stretched again to load the unprocessed wafer into the process chamber. At this time, the pick portion 10B is advanced to load the unprocessed wafer held by the pick portion 10B into the process chamber. The emptied pick portion 10B is retreated, thus completing the transfer operation.
The following patent documents 2 and 4 disclose other types of transfer apparatuses. In each of these transfer apparatuses, a pair of picks each for holding a wafer are arranged not in one horizontal plane but to overlap vertically, unlike in patent documents 1 and 3, and are set to face the same direction. Three motors are used as a driving source to pivot the entire apparatus and advance and retreat the respective picks.
[Patent document 1] U.S. Pat. No. 5,899,658
[Patent document 2] Jpn. Pat. Applin. KOKAI Publication No. 2000-72248
[Patent document 3] Jpn. Pat. Applin. KOKAI Publication No. 7-142551
[Patent document 4] Jpn. Pat. Applin. KOKAI Publication No. 10-163296
The transfer apparatuses shown in FIG. 33, patent documents 1 and 3, and the like have the following problems. To exchange a processed wafer and unprocessed wafer in the process chamber, the pick arm 10 must be pivoted through 180°. This large pivot angle leads to a waste of time and accordingly swift exchange operation cannot be performed. In particular, as the wafer size increases from a diameter of 200 mm to 300 mm, the wafer weight increases, so the pivot speed cannot be increased. Further, when the arm 8 extends and contracts, either one pick always holds a wafer. Thus, the extending/contracting speed of the arm 8 cannot be increased very much. In each of the transfer apparatuses disclosed in patent documents 2 and 4, three motors are necessary as a driving source, and the apparatus cost rises accordingly.